My theory of the Domination cancelation after watching the new documentary:
Britney wanted to cancel domination and refuse to work because she wanted to try to end the conservatorship. She was sick of their empty promises if she kept cooperating. As a reaction to her discussing ending Domination, her Dad's team said Britney's meds must be off, she's not thinking clearly, let's try one more time to get her to cooperate.
The night of the Domination announcement she was forced to go on stage, but she didn't want to say anything verbally to promise her fans She would be doing a new residency, because she already knew, no matter what, She wouldn't commit to Domination. Her not speaking was a total shock to her team.
Her team later decided they would indeed have to cancel the show, and her dad's team used Jamie's health as an excuse to give the public a reason that wouldn't hurt her long term image as much.
The reason given from the leaked voicemail (about her meds needing to be adjusted) was the reason Jamie's team told the conservatorship team, and they pushed her into rehab as a result. Not necessary as punishment, but so they could say afterwards that she was treated and better, and now stable enough to make future work commitments.
I'm sure Britney was in a fragile state just because of the stress of ending that new residency, being pissed at her team, etc. She may not have wanted treatment initially but knew she had to go and look good in the eyes of doctors to get back on track slightly towards freedom. If she lost her **** she would be trapped forever. Then in treatment she concluded in a mature manner she would like to go on indefinite hiatus, and told them she was done working. And they would need to hire a financial planner instead of Jaime to manage her retirement funds since she would no longer be bringing in all that money.
I believe she's at a stand still with them. If she gets her freedom, she may decide to work a bit more. However they don't want her to work again unless it makes THEM money too, so they don't want to release her. It's sad.